A method for producing ammonium fluoride and co-producing silica using fluorosilicic acid
By preparing SiO2 seed crystals through oblique upward spraying and mixing of fluorosilicic acid and ammonia, the problems of uneven mixing and equipment complexity were solved, and the uniformity of silica particle size and production efficiency were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DO FLUORIDE CHEM CO LTD
- Filing Date
- 2024-05-17
- Publication Date
- 2026-07-31
AI Technical Summary
In the existing technology for preparing fluorosilicic acid by reacting it with ammonia, uneven mixing and strong stirring lead to uneven seed crystal quality, which affects the uniformity of the silica product and the production efficiency. In addition, the equipment is complex and prone to clogging, which also affects the production efficiency.
Fluorosilicic acid and ammonia are mixed by spraying from an angle upwards, with the pH value controlled at 6-7. After standing for 30-300 minutes, SiO2 seed crystals are prepared. Subsequently, they are mixed in a continuous flow reactor at a pH value of 8-9, with the seed crystal amount being 10-40%. Vigorous stirring is avoided. The preparation equipment is simple and easy to maintain.
It achieves good seed crystal suspension, uniform silica particle size, high production efficiency, less equipment clogging, convenient maintenance, and excellent product quality.
Smart Images
Figure CN118495557B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of comprehensive utilization technology of fluorosilicic acid, specifically relating to a method for producing ammonium fluoride and co-producing silica from fluorosilicic acid. Background Technology
[0002] Fluorosilicic acid, a byproduct of wet-process phosphate fertilizer production, is an important fluorine resource. Especially after restrictions on fluorite mining, many fluorine-related companies have begun to focus on utilizing fluorosilicic acid. There are multiple utilization pathways, such as the cryolite production method (fluorosilicic acid + sodium hydroxide + aluminum hydroxide), the aluminum fluoride production method (fluorosilicic acid + aluminum hydroxide), the ammonium fluoride production method (fluorosilicic acid + ammonia), and the hydrogen fluoride production method (fluorosilicic acid + concentrated sulfuric acid). Among these, cryolite and aluminum fluoride are mainly used in the electrolytic aluminum industry, with a relatively small market capacity. The hydrofluoric acid production method (reacting with concentrated sulfuric acid) generates large amounts of fluorinated dilute sulfuric acid, creating a new burden. Comparatively, the reaction with ammonia to produce ammonium fluoride is the most efficient. Ammonium fluoride is widely used in etching agents and preservatives, and can also be further processed into anhydrous hydrogen fluoride. For example, patent CN114804030A uses fluorosilicic acid and ammonia to react to obtain ammonium fluorosilicate solution. The ammonium fluorosilicate solution reacts with ammonia and is concentrated and thermally decomposed to obtain molten ammonium hydrogen fluoride liquid. The molten ammonium hydrogen fluoride liquid reacts with sodium fluoride and is cooled and crystallized to obtain sodium hydrogen fluoride ointment. The sodium hydrogen fluoride ointment is dried and thermally decomposed to obtain crude hydrogen fluoride gas, which is then purified to obtain anhydrous hydrogen fluoride.
[0003] In the ammoniation reaction of fluorosilicic acid and ammonia, a crucial step is the preparation of seed crystals. The quality of these seed crystals directly affects the efficiency of subsequent ammoniation reactions and the quality of the byproduct silica. Typically, rapid mixing of fluorosilicic acid and ammonia is required, along with controlling the pH value at the reaction endpoint. This process demands both uniform mixing and avoids vigorous stirring, as the seed crystals are suspended, three-dimensional network-structured SiO2 grains. Inhomogeneous mixing leads to uneven grain growth, affecting the uniformity of the silica product's grain size. Vigorous stirring, on the other hand, disrupts the network structure, causing precipitation and affecting suspension. Patent CN112758956A utilizes a tubular reactor, dispersing the reaction within numerous fine tubes, which improves uniformity to some extent. However, this method is complex, difficult to maintain in practice, and impacts production efficiency. Summary of the Invention
[0004] The inventors of this application have overcome the above-mentioned shortcomings and innovatively implemented a method for preparing SiO2 seed crystals. This seed crystal is suitable for the ammonialation of fluorosilicate to produce ammonium fluoride and concurrently produce silica. The resulting silica has uniform crystal grains, simple equipment, and high production efficiency.
[0005] A method for producing ammonium fluoride and co-producing silica using fluorosilicic acid includes the following steps:
[0006] (1) Spray fluorosilicic acid solution and ammonia water obliquely upwards respectively. After the two droplets converge and mix, they fall into a container and are left to stand to obtain SiO2 seed suspension.
[0007] (2) The seed suspension obtained in (1) is mixed with fluorosilicic acid solution and ammonia water to react and obtain a mixture of silica and ammonium fluoride;
[0008] (3) The mixture obtained in (2) is filtered by hydraulic pressure. The filter cake is washed and dried to obtain white carbon black. The filtrate is concentrated and crystallized to obtain ammonium fluoride.
[0009] In step (1), the spray flow rate of fluorosilicic acid solution and ammonia water is controlled with reference to the pH value of the mixture, and the target pH value of the mixture is 6-7.
[0010] In step (1), the two droplets move obliquely upwards and gradually decelerate, converging at their minimum speed. This ensures thorough mixing while minimizing shear force. It should be noted that SiO2 begins to form as soon as the two liquids come into contact. Strong shearing at this point can affect the formation of a network structure between the grains and cause the grains to collide and aggregate, resulting in larger grains. Both of these situations are undesirable. The angle between the upward spray direction and the horizontal plane is 45-89°, more preferably 60-70°. The preferred settling time is 30-300 minutes. During this period, the grains gradually grow from sub-nanometer to nanometer scale, appearing macroscopically as a thin gel and microscopically as a three-dimensional network.
[0011] The mixing reaction in step (2) is preferably carried out in a continuous flow reactor, with the final pH value of the three solutions being 8-9, and the amount of seed crystals being 10-40% of the theoretical yield of silica.
[0012] The ammonium fluoride solution obtained in step (3) can also be heated to prepare ammonium hydrogen fluoride, which can then be further processed into hydrogen fluoride.
[0013] The concentration of the fluorosilicic acid solution is 15-22%, preferably derived from phosphate fertilizer by-products; the concentration of the ammonia water is 300-340 g / L; the temperature is controlled to be ≤45℃ during the reaction process in step 2).
[0014] The beneficial effects of this invention are as follows: The fluorosilicic acid solution and ammonia water are mixed in the form of droplets to prepare seed crystals, resulting in good mixing uniformity. No strong stirring is required throughout the process, thus preserving the network structure of the seed crystals. The equipment used for seed crystal preparation has a simple structure, is not easily clogged, and is easy to maintain. The resulting seed crystal suspension has good suspension properties and exhibits good crystallization induction during the fluorosilicic acid ammoniation reaction. Because the seed crystals have uniform particle size, the resulting silica product also has a uniform particle size, leading to better performance in later applications. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of a mist droplet spray. In the diagram, 1 represents the horizontal plane, 2 represents the direction of the mist droplet spray, and 3 represents the angle between the direction of the mist droplet spray and the horizontal plane. Detailed Implementation
[0016] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.
[0017] Example 1
[0018] A method for producing ammonium fluoride and co-producing silica using fluorosilicic acid:
[0019] (1) Spray a 15wt% fluorosilicic acid solution and a 300g / L ammonia solution, which are by-products of phosphate fertilizer enterprises, at an angle of 60° to the top, with flow rates of 2000g / min and 700ml / min, respectively. After the two droplets converge and mix, they fall into a container with a pH of 6.5. After standing for 5 minutes, a SiO2 seed suspension is obtained.
[0020] (2) Take 1000g of the seed solution obtained in (1), 2200g of fluorosilicic acid solution with 15wt% fluorosilicic acid and appropriate amount of ammonia water and slowly add them to the continuous flow reactor. The pH of the mixture is 8.5. After reacting for 30 minutes, white carbon black and ammonium fluoride solution are obtained.
[0021] (3) The mixture obtained in (2) was filtered by hydraulic filtration. The filter cake was washed with pure water and dried to obtain 402g of white carbon black. The filtrate was concentrated and crystallized to obtain 639g of ammonium fluoride.
[0022] Example 2
[0023] A method for producing ammonium fluoride and co-producing silica using fluorosilicic acid:
[0024] (1) Spray a 22wt% fluorosilicic acid solution and a 340g / L ammonia solution at an upward angle of 50° and 45° respectively, with flow rates of 1500g / min and 730ml / min respectively. After the two droplets converge and mix, they fall into a container with a pH of 6.9. After standing for 15min, a SiO2 seed suspension is obtained.
[0025] (2) Take 1000g of the seed solution obtained in (1), 3360g of fluorosilicic acid solution with 22wt% fluorosilicic acid and an appropriate amount of ammonia water and slowly add them to the continuous flow reactor. The pH of the mixture is 9.0. After reacting for 120 minutes, white carbon black and ammonium fluoride solution are obtained.
[0026] (3) The mixture obtained in (2) was filtered by hydraulic filtration. The filter cake was washed with pure water and dried to obtain 855g of white carbon black. The filtrate was concentrated and crystallized to obtain 1357g of ammonium fluoride.
[0027] Example 3
[0028] A method for producing ammonium fluoride and co-producing silica using fluorosilicic acid:
[0029] (1) Spray 18wt% fluorosilicic acid solution and 320g / L ammonia water at an upward angle of 70° and 65° respectively, with flow rates of 1200g / min and 440ml / min respectively. After the two droplets converge and mix, they fall into a container with a pH of 6.0. After standing for 100min, a SiO2 seed suspension is obtained.
[0030] (2) Take 1000g of the seed solution obtained in (1), 2930g of fluorosilicic acid solution with 18wt% fluorosilicic acid and an appropriate amount of ammonia water and slowly add them to the continuous flow reactor. The pH of the mixture is 8.0. After reacting for 300min, white carbon black and ammonium fluoride solution are obtained.
[0031] (3) The mixture obtained in (2) was filtered by hydraulic filtration. The filter cake was washed with pure water and dried to obtain 716g of white carbon black. The filtrate was concentrated and crystallized to obtain 1114g of ammonium fluoride.
[0032] Comparative Example 1
[0033] A method for producing ammonium fluoride and co-producing silica using fluorosilicic acid, which avoids the spray mixing method and instead uses a direct liquid mixing method to prepare SiO2 seed crystals:
[0034] (1) 2000g of 18wt% fluorosilicic acid solution and 733mL of 320g / L ammonia solution were directly and quickly mixed, stirred slightly, and the pH was 6.0. After standing for 100min, SiO2 seed suspension was obtained.
[0035] (2) Take 1000g of the seed solution obtained in (1), 2930g of fluorosilicic acid solution with 18wt% fluorosilicic acid and an appropriate amount of ammonia water and slowly add them to the continuous flow reactor. The pH of the mixture is 8.0. After reacting for 300min, white carbon black and ammonium fluoride solution are obtained.
[0036] (3) The mixture obtained in (2) was filtered by hydraulic filtration. The filter cake was washed with pure water and dried to obtain 703g of white carbon black. The filtrate was concentrated and crystallized to obtain 1098g of ammonium fluoride.
[0037] Comparative Example 2
[0038] A method for producing ammonium fluoride and co-producing silica using fluorosilicic acid still employs the spray convergence method, but with a smaller upward spray angle:
[0039] (1) Spray 18wt% fluorosilicic acid solution and 320g / L ammonia water at an upward angle of 30°, respectively, with flow rates of 1200g / min and 440ml / min. The two droplets converge and mix in opposite directions and fall into a container with a pH of 6.0. After standing for 100min, a SiO2 seed suspension is obtained.
[0040] (2) Take 1000g of the seed solution obtained in (1), 2930g of fluorosilicic acid solution with 18wt% fluorosilicic acid and an appropriate amount of ammonia water and slowly add them to the continuous flow reactor. The pH of the mixture is 8.0. After reacting for 300min, white carbon black and ammonium fluoride solution are obtained.
[0041] (3) The mixture obtained in (2) was filtered by hydraulic filtration. The filter cake was washed with pure water and dried to obtain 695g of silica. The filtrate was concentrated and crystallized to obtain 1090g of ammonium fluoride.
[0042] Experimental Example
[0043] The particle size distribution of the silica products obtained in Examples 1-3 and the comparative example was determined using a BOS-1076-A fully automatic laser particle size analyzer. The data are listed below:
[0044] Spray angle (°) <![CDATA[D 10 (μm)]]> <![CDATA[D 90 (μm)]]> Distribution width (μm) Example 1 60 2.2 4.4 2.2 Example 2 50，45 1.5 4.3 2.8 Example 3 70，65 1.9 4.4 2.5 Comparative Example 1 / 1.0 5.1 4.1 Comparative Example 2 30 1.1 6.8 5.7
[0045] The test results show that in Experiments 1-3, the silica obtained using the technical solution of this invention has a smaller particle size distribution and better uniformity. In Comparative Example 1, the SiO2 seed crystals were prepared using a direct liquid mixing method, resulting in a larger particle size distribution and poorer uniformity. In Comparative Example 2, the spray direction had a smaller angle with the horizontal plane, so the angle formed when the two droplets converged was larger, resulting in a larger horizontal velocity component. The convergence of the droplet streams generated strong shearing, resulting in a poor seed crystal network structure and large differences in crystal diameter, thus leading to a wider particle size distribution and poor uniformity.
Claims
1. A method for producing ammonium fluoride co-producing white carbon black using fluosilicic acid, characterized by, The method includes the following steps: (1) Spray fluorosilicic acid solution and ammonia water separately upward at an angle. After the two droplets converge and mix, they fall into a container and are left to stand to obtain a SiO2 seed suspension. The angle between the upward spray direction and the horizontal plane is 45-89°. (2) The seed suspension obtained in (1) is mixed with fluorosilicic acid solution and ammonia water to react and obtain a mixture of silica and ammonium fluoride; (3) The mixture obtained in (2) is filtered by hydraulic filtration. The filter cake is washed and dried to obtain white carbon black. The filtrate is concentrated and crystallized to obtain ammonium fluoride.
2. The method of claim 1, wherein, In step (1), the angle between the upward spray direction and the horizontal plane is 60-70°.
3. The method of claim 1, wherein, The two droplet streams mentioned in step (1) converge when their velocity is at its minimum.
4. The method of claim 1, wherein, The pH value of the two droplet streams after mixing in step (1) is 6-7, and the settling time is 30-300 min.
5. The method of claim 1, wherein, The final pH value of the mixture of the seed suspension, fluorosilicic acid solution, and ammonia in step (2) is 8-9.
6. The method of claim 1, wherein, The amount of seed crystals used in step (2) is 10-40% of the theoretical yield of silica.
7. The method of claim 1, wherein, In steps (1) and (2), the concentration of fluorosilicic acid solution is 15-22%, and the concentration of ammonia water is 300-340 g / L; the temperature is controlled to be ≤45℃ during the reaction process in step (2).
8. The method of claim 1, wherein, Step (2) is carried out in a continuous flow reactor.